Water Supply Outlook Report for February

General Outlook: February brought an interesting mix of good high mountain snow and record precipitation. Snowpack remains healthy but the big story was the major flooding in the Umatilla River in North East Oregon and on Mill Creek, Walla Walla and Touchet rivers in South East Washington. Catastrophic damage was reported for roads, livestock facilities and farmland. Record precipitation was also recorded in the West Central Cascades however west side rivers have evolved to handle such large flows, so flood damage was minimum and mostly inconvenient. The most recent forecast through mid-March shows a high probability for below normal temperatures and a mixed bag of normal to below normal precipitation. NWS 3-month (MAM) forecast indicates above normal temperatures on the west side and equal chances for above, below or normal temperatures east of the Cascades. Precipitation is forecasted to have equal chances. The US Drought Monitor indicates D0-D1 drought designation shrinking from last month however still persistent North to South in Central Washington, most likely due to the lack of precipitation and low elevation snow through most of the region.

Snowpack: The March 1 statewide SNOTEL readings were 107% of normal. The lowest readings in the state were at 67% of the 30-year median for March 1 in the Conconully Lake area. The Cowlitz River Basin had the most snow with 130%. Westside medians from SNOTEL, and March 1 snow surveys, included the North Puget Sound river basins with 112% of normal, the Central and South Puget river basins with 106% and 116% respectively, and the Lower Columbia basins with 110% of normal. Snowpack along the east slopes of the Cascade Mountains included the Yakima area with 108% and the Wenatchee area with 102%. Snowpack in the Spokane River Basin was at 107% and the Upper Columbia river basins had 100% of the long-term median.

Precipitation: February precipitation from SNOTEL varied greatly with amounts as low as 33% of average at Upper Wheeler SNOTEL to as high as 255% of average in the Walla Walla Basin. Skookum Creek SNOTEL in the Tolt River Basin received the most precipitation with 29.8” or 255% of normal. Sourdough Gulch SNOTEL in Asotin County had the highest percentage at 488% of the long-term average.

Reservoir: Seasonal reservoir levels in Washington can vary greatly due to specific watershed management practices required in preparation for irrigation season, fisheries management, power generation, municipal demands and flood control. March 1 Reservoir storage in the Yakima Basin was 460,000-acre feet, 102% of average for the Upper Reaches and 166,000-acre feet or 121% of average for Rimrock and Bumping Lakes. The power generation reservoirs included the following: Coeur d’Alene Lake, 65,000-acre feet, 49% of average and 27% of capacity; and Ross lake within the Skagit River Basin at 95% of average and 56% of capacity. Recent climate impacts and management procedures may affect these numbers on a daily or weekly basis.

Streamflow: As we near the apex of winter we can see an increase in streamflow forecast accuracy. However late winter and even spring climate conditions may warrant changes as we move forward. Volumetric forecasts are developed using current, historic and average snowpack, precipitation and streamflow data collected and coordinated by organizations cooperating with NRCS. Caution should be used when using early season forecasts for critical water resource management decisions since governing conditions are likely to change for the better or the worse.